Quality and condition monitoring based on spectrum separating measurement

ABSTRACT

The invention relates to a method in the process of manufacturing and/or finishing a fibre web, in which method said continuous and moving web, and/or a moving means related to the processing of the web, is monitored by at least one optical spectrum separating measurement device to determine at least one quality variable of said object for the purpose of controlling the quality or condition. According to the invention, spectral data is collected in synchronization with the movement from the object which is being examined and is in a progressive and/or rotating movement, by measuring electromagnetic radiation, which has been transmitted, reflected, or otherwise emitted by the object, in a temporally and spatially resolved manner. On the basis of this spectral data, a two-dimensional quality variable chart is formed, which is substantially continuous in the direction of movement of the object and presents at least one quality variable of the object, and in order to determine the characteristics of the object and/or to detect defects in the object from said continuous quality variable chart, local deviations and/or discontinuities are detected in said continuous quality variable chart, especially in the direction of movement. The cause of these deviations and/or discontinuities is identified on the basis of the periodicity of said phenomena in the direction of movement.

FIELD OF THE INVENTION

The invention relates to a method for controlling quality and conditionon the basis of spectrum separating measurement, to be used inconnection with processes of manufacturing or finishing a continuousfibre web, particularly a paper web, according to the preamble of theappended claim 1.

BACKGROUND OF THE INVENTION AND PRIOR ART

In the manufacturing and finishing processes of paper, paperboard andother corresponding web-like materials, the significance of methods andsystems monitoring the web as such and/or the process in real timeincreases continuously when the aim is to achieve as high a productioncapacity as possible and a high and equal quality of the product.

The use of optical methods is a method, which has been found to be veryefficient in implementing real-time monitoring of a rapidly moving fibreweb and its path. Advantages of optical methods include, for example,the possibility to perform measurements of the object in a contactlessmanner and to perform measurements with a rapid time response. Severalexamples of applying optical methods in the manufacturing and finishingprocesses of web-like materials are known from prior art.

In so-called imaging methods, i.e. methods which produce a visual imageof an object and which are known from prior art, the object is typicallyrecorded with matrix or line scan cameras, which are based on CCDtechnology (Charged Coupled Device) and thus operate on a substantiallyvisible wavelength range. Imaging measurements may be performed as localmeasurements, but nowadays also as measurements monitoring the fibre webacross its entire production width. Prior art is described, for example,in the conference publication “Paper Machine Applications with FullsheetImaging Measurement” (Chen Shih-Chin et al, Control Systems '98:Information tools to match the evolving operator role, pages 330 to 337,Porvoo, Finland, Sep. 1 to 3, 1998). In imaging measurements, the useraims at recognizing visually detectable abnormal phenomena and theircauses in the object from the image either by him/herself or with thehelp of computer image processing.

In addition to the imaging diagnostics, which operates on the visiblerange, prior art also recognizes the use of thermal cameras operating inthe infrared range for monitoring the fibre web and its path.

Prior art further recognizes optical methods based on spectralseparation as well, wherein the characteristics of the object, e.g.paper web, are determined quantitatively by measuring and analysingcertain wavelength bands (spectral bands) included by the light emitted,transmitted or reflected by the object, or a more continuous wavelengthdistribution of the light (continuous spectrum). It is particularlytypical for spectrum separating methods that they utilize the spectralcharacteristics of the light measured from the object, or, moregenerally of the electromagnetic radiation, to determine a certainquality variable. In methods based purely on imaging, the detection oflight typically occurs without actual spectrum separation by using onlyone wavelength band, which wavelength band is often determined accordingto the wavelength sensitivity of the detector.

Because the abovementioned methods, which are based on spectrumseparation, can be considered to represent the closest prior art fromthe point of view of the current invention, they will be discussed inmore detail in the following.

U.S. Pat. No. 4,733,078 presents equipment for measuring the moisturelevel of a paper web, wherein radiation from the infrared range isdirected from a light source through the paper web in such a manner thatthe radiation, which has penetrated the paper web, is measuredsuccessively in time on several spectral bands to determine the moisturelevel of the paper web. An obvious problem of this solution is thedifference in time of the measurements taken on different spectralbands, in which case when using data measured on different spectralbands at different times for determining the moisture level of the web,the measurement result obtained in this manner does not describe acertain point of the web exactly, but the measurement result isnaturally affected by the movement of the web during the measurement.

U.S. Pat. No. 3,641,349 discloses equipment, in which radiation of theinfrared range, which has penetrated a paper web, is divided intoseveral optical branches, each optical branch being directed through aseparate wavelength filter to a separate detector. By modulating theradiation directed through the paper web in a suitable manner, it ispossible to perform the measurement simultaneously on all the examinedspectral bands, i.e. in a temporally parallel manner, in which case themoisture value of the web, obtained as a result of the measurement,better represents a certain local range of the web. One limitation ofthe method is that the number of spectral bands being examined is, inpractice, limited, because the complexity of the measurement equipmentincreases significantly with an increase in the number of spectralbands. Because of the number of detectors the costs of measurementequipment can also be high.

The applicant's previous patent application WO 99/14579, which hasbecome public, further discloses measurement equipment, wherein infraredradiation is directed from the light source through a moving paper web,and the radiation, which has penetrated the paper web, is further led toa spectrograph for spectrum separation. By means of this arrangement itis possible to measure, instead of a few separate spectral bands, a morecontinuous spectrum of the radiation with the help of a matrix detectorinstalled on the output level of the spectrograph. Thus, in themeasurement, all the examined so-called wavelength channels are measuredat the same time, i.e. temporally in parallel with each other. Thus, asthe measurement result the momentary continuous spectrum of themeasuring point can be determined in a certain wavelength range, inwhich case the accuracy of determining the characteristics of an object,such as the moisture level of the web or other examined qualityvariable, on the basis of the aforementioned spectral data, is betterthan when determining the quality variable on the basis of only a fewspectral bands, which are measured, for example, by using separate andparallel optical filters.

U.S. Pat. No. 5,019,710 discloses equipment, by means of which themeasurement based on spectral separation can be performed across theentire cross-directional width of the fiber web without needing totraverse the optical measurement device, i.e. to move it mechanically incross-direction of the web. The solution presented in the U.S. Pat. No.5,019,710 is based on the use of optical fibres in such a manner thatthe measuring point is traversed for different points in thecross-direction of the web by multiplexing the optical device, whichperforms the actual measurement and comprises a light source and adetector part, to optical fibre pairs arranged at different points ofthe web, in which optical fibre pairs one of the optical fibres placedon different sides of the web conducts light from the light source tothe web, and correspondingly the other conducts the light from the webto the detector part.

Furthermore, publication WO 99/02941 presents the measuring of thethickness of a paper web in such a manner that a measuring beam is ledto the paper web with optical fibres, and the radiation, which haspenetrated the web, is further conducted to an optical measurementdevice. In this solution, the optical fibres are arranged side by sidein the cross-direction of the web substantially across the whole widthin the transverse direction of the web. According to one embodimentpresented in said publication, measurement of the continuous spectrum inthe cross-direction of the web in all measuring points is performedsimultaneously by means of parallel miniature spectrometers.

In a summary, it can be stated that by using the arrangements of priorart in order to determine the characteristics of the web, it is possibleto implement different kinds of spectrum separated optical measurementsin such a manner that the measurements cover substantially the entirecross-directional width of the web and either individual spectral bandsor a continuous wider spectral range is measured at each measuringpoint. Temporally, the measurement can be implemented in such a mannerthat the measurement of the cross-directional profile of spectral datais implemented in the transverse direction of the web at all measuringpoints substantially at the same time (without traversing), and at eachmeasuring point all the wavelengths being monitored are registeredsubstantially at the same time (in a temporally parallel manner).

In the above-described spectrum separated measurements according toprior art, the time elapsed in the measuring, during which time the webbeing examined thus continuously travels past the monitoring point, is,according to the opinion of the applicant, discussed only in thefollowing senses in the development of measurement methods. Firstly,there is an aim to develop the measurement methods in such a manner thatthe measurement information is registered simultaneously across theentire width in the transverse direction of the web without mechanicaltraversing or the like. The aim is thus for the measurement toefficiently cover the entire area of the web. Secondly, there is an aimto develop the measurement methods in such a manner that the individualspectral bands or the continuous spectrum being examined in eachcross-direction measuring point of the web are to be measured temporallyat the same time, in which case an interesting characteristic of the webthat is to be determined by using them, such as moisture, representssaid point of the web more accurately without the movement of the webaffecting the measurement result.

BASIC PRINCIPLE AND MOST IMPORTANT ADVANTAGES OF THE INVENTION

The primary aim of the present invention is to provide a novel methodfor controlling quality and condition on the basis of spectrumseparating measurement, to be used in processes for manufacturing and/orfinishing a continuous fibre web.

The aim of the invention is to utilize, significantly more efficientlythan in prior art, the possibility to perform optical spectrum separatedmeasurements on the web or its path, with a good temporal and spatialresolution. The aim of the invention is thus further to make it possibleto collect significantly more diverse and detailed data from an objectbeing measured than with prior art methods, and further to automaticallyanalyse the measurement results significantly more efficiently with acomputer or the like.

It is a particular aim of the invention to make it possible to observemore accurately than in prior art, and reliably identify fast phenomena,which appear only momentarily in the so called machine direction in theprocess. The invention is also applicable, however, for analysing morecontinuous phenomena. A very significant advantage of the invention isthat the cause of failures in the process can now be identified by meansof the invention in an easier and more reliable way than in prior art.Thus, the invention makes it possible to implement a highly automatedcontrol of quality and condition.

To attain these purposes, the method according to the invention isprimarily characterized in what will be presented in the characterizingpart of the independent claim 1.

The other, dependent claims will present some preferred embodiments ofthe invention.

The essential basic idea of the invention is that temporally andspatially resolved spectral data is collected with the optical spectrumseparating measurement device from a moving object, i.e. a web or anelement involved in handling it, in a manner synchronized with themovement of said object. On the basis of this spectral data, atwo-dimensional “quality variable chart” is formed, which chart isfurther substantially continuous in the direction of movement anddescribes at least one quality variable.

In this context, the two-dimensional quality variable chart refers to amethod of storing data, in which the data is stored in a coordinatesystem, its first axis describing a point in the cross-direction of theobject (such as, for example, the web), and the second axis of thecoordinate system describing a point in the direction of movement of theobject. At each point, which is determined with the help of said twocoordinates data on the value of said quality variable is stored.

Said quality variable can be, for example, the moisture level of the webor the amount of coating of the web, which quality variables aredetermined from the web on the basis of, for example, transmission andspectrum separated reflection measurements, which are carried out on theinfrared range. Thus the quality variable chart reveals, for example,changes in the moisture level of the web at different points of the webin machine direction and cross-direction.

The quality variable being examined can also be another characteristicof the web, the coating of the web or an element connected to thehandling of the web, which is determined, for example, by means ofspectrum separated measurements performed on the visible range. Thequality variable can thus be, for example, the colour, opacity,brightness, gloss, or smoothness of the object.

According to the invention, to determine the characteristics of theobject and/or in order to detect defects in the object, local deviationsand/or discontinuities, especially in the direction of motion of theobject, of at least one quality variable are further recognized in saidcontinuous quality variable chart, and the cause of such deviancesand/or discontinuities is recognized on the basis of the periodicity ofsaid phenomena in the direction of the movement.

Thus, synchronizing the two-dimensional quality variable chart with themovement of the object will make it possible to detect, in the qualityvariable chart, recurrent and transient phenomena in the machinedirection, in an efficient and, if necessary, automatic way, andfurthermore, the causes of these recurrent phenomena can be identifiedon the basis of the periodicity of the phenomena.

If the object to be measured is, for example, a moving fibre web, thecause of a defect recurring at regular intervals in the web can beidentified to be a roll rotating at a known peripheral speed in relationto the web, wherein a damaged or soiled point on the surface of the rollcauses a defect in the passing web, recurring at intervals correspondingto the peripheral length of said roll.

In an advantageous embodiment of the invention, the quality variablechart formed of the object or the spectral data used in forming it isaveraged in the machine direction across a cycle length specific to theobject to be monitored, in order to detect periodical phenomena of lowerintensity. The cycle length to be used in the averaging can be selectedto correspond, for example, to the peripheral length of a specific roll.Averaging efficiently removes random noise present in the measurementresult.

By using the method according to the invention, it is possible tosearch, in the quality variable chart, for periodical phenomena causedby the object to be measured, or by a component preceding it in theprocess. Thanks to the collecting of spectral data at good sensitivity,and averaging of the results, it is also possible to detect periodicalphenomena in the fibre web, which are caused by (preceding) componentslocated farther away from the point of measurement. As a result, it ispossible to monitor more steps (a longer web length) in the process byusing only a single measuring point.

The method according to the invention can be applied for monitoring themoving web itself, or for monitoring the condition of rotating/movingmeans which are involved in the processing of the web and are in contactwith it, such as rolls and various textures (wires, felts). Theinvention is also applicable for monitoring the properties of reels tobe formed of the web.

A malfunction of the means involved in the processing of the fibre webcan be detected either by direct measurement of said means or on thebasis of a marking caused in the passing web by said means.

The measurement according to the invention can be carried out inrelation to the direction of movement of the object being examinedacross the entire width in the transverse direction of the object oronly partly across said width. When measuring across the entire width ofthe object, for example a fibre web, the measurement is carried outadvantageously by using such a measurement arrangement, where themeasurement of the cross-direction profile of the spectral data iscarried out substantially at the same time across the entire width ofthe web. Thus the phenomena occurring in the cross-direction in relationto the direction of movement of the object and in the machine directionaccording to the movement can be reliably distinguished from each other.

The following more detailed description of the invention with exampleswill more clearly illustrate, for anyone skilled in the art, preferredembodiments of the invention as well as advantages to be achieved withthe invention in relation to background art.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail withreference to the appended drawings, in which

FIG. 1 shows some possible embodiments of the invention in principle,

FIG. 2 shows a spectrum separating measurement device applied in themethod according to the invention in principle,

FIG. 3 shows the operating principle of a spectrometer applicable in themeasurement device according to FIG. 2 in principle,

FIG. 4 illustrates a continuous two-dimensional quality variable chartformed according to the invention in principle,

FIG. 5 shows, in principle, a matched quality variable chart obtainedfrom the continuous quality variable chart of FIG. 4 by averaging acrossa given interval, and

FIG. 6 shows, in principle, a matched quality variable chart obtainedfrom the continuous quality variable chart of FIG. 4 by averaging acrossanother interval.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows, in principle, some possible embodiments, which correspondto the different placements A, B, C of the spectrum separatingmeasurement device marked in FIG. 1. The invention will be discussed inthe following by using the placement A marked in FIG. 1 as an exampleand the moisture level of web 11 as the quality variable being examined.

A spectrum separating measurement device 10 placed in position A isarranged to collect spectral data from the moving web 11 being measuredin order to form a continuous quality variable chart of the web 11according to the invention. The web 11 can be a fibre web, which canappear in different forms in paper or board manufacturing, and whichcan, depending on the measuring point be supported from the measuringpoint also in relation to the measurement device 10 from the oppositeside by means of a wire, a roll or another element.

FIG. 2 shows a possible embodiment of a spectrum separating measurementdevice 10 in principle. The measurement device 10 comprises a radiationsource 20, which emits radiation preferably in the infrared range whenthe quality variable is the moisture level of the web. The wavelength ofthe radiation can be, for example, between 1 to 2.5 μm, but ifnecessary, the wavelength can be shorter or longer than this, dependingon the quality variable being examined. The radiation source can be, forexample, a radiator of a black body, a halogen lamp, or anotherradiation source suitable for the purpose.

When the measurement is taken in the infrared range, there are, ifnecessary, breaks 21 arranged after the radiation source 20 to break ormodulate the radiation in time in a way known as such. Radiation fromthe radiation source 20 is led to an object 11, 16, 17 by means of firstoptical fibres 23. Said object can be, as shown in FIG. 1, the paper web11 as such or another element related to its processing, such as a roll16 or a wire cloth 17. Radiation reflected from the object 11, 16, 17 isfurther led with second optical fibres 24 to a spectrometer 25.

The ends of both the first optical fibres 23 and the second opticalfibres 24 are arranged at measurement ends 26. In addition, at there canbe other necessary measurement optics, such as lens or mirrorarrangements for controlling the radiation between the ends of theoptical fibres 23, 24 and the object 11, 16, 17, arranged at themeasurement ends. The measurement ends 26 determine the parallelmeasuring points 28 in the cross-direction of the object, which arebeing used in the measurement.

The spectrometer 25 comprises according to FIG. 3, at least aspectrograph 30 and a matrix detector 31. The spectrograph 30 isarranged to record light radiation directed from other optical fibres 24to its entrance port 32 in a matrix detector 31 in such a spectrallyseparated manner that in the direction Y marked on FIG. 3 a point axisis formed on the matrix detector 31 and correspondingly in direction X awavelength axis. Thus, for example, radiation from fibre 24 a, whichbelongs to the second optical fibres, is imaged as spectrum 24 b on thematrix detector 31, in which spectrum the different wavelengths from thelongest wavelength λ₁ to the shortest wavelength λ₂ are divided intodifferent points of the matrix detector 31 in the direction of thewavelength axis X. Correspondingly, for example, the radiation from asecond optical fibre 24 c is imaged as spectrum 24 d on the matrixdetector. The spectrograph 30 can be, for example, a PGP-typespectrograph (Prism-Grating-Prism), a grating spectrograph, or anotherprior art device suitable for the use.

Thus, the spectrum separating measurement device 10 makes it possible tomeasure spectral data on the object 11, 16, 17 in relation to thedirection of movement of the object in the cross-direction at severalparallel measuring points simultaneously in time. Thus, the momentarycross-directional profile of the spectral data of the object isdetermined with the measurement device. When the quality variabledetermined according to the spectral data is, for example, the moisturelevel, the spectral data is measured preferably in the near infraredrange, for example in the wavelength range from 1.0 to 1.7 μm or from1.0 to 2.4 μm.

The continuous two-dimensional quality variable chart according to theinvention is thus formed by means of cross-direction profiles of thespectral data, which are determined from the object at successivemoments of time. An individual cross-directional profile of spectraldata comprises parallel measuring points in cross-direction, wherein ateach parallel measuring point, a continuous spectrum of the object on acertain range is stored substantially at the same time by means of, forexample, a spectrograph, or several separate spectral bands are storedby using, for example, parallel optical filters.

When the quality variable being measured is, for example, the moisturelevel of the web 11, the continuous two-dimensional quality variablechart according to the invention thus describes the changes in themoisture level of the web 11 in a spatially resolved manner both in thecross-direction and the machine direction of the web 11.

In order to implement the quality and condition monitoring according tothe invention, the spectrometer 25, which automatically collectsspectral data, is arranged according to what is presented in FIG. 2 in adata transmission connection with a data processor 27. In the dataprocessor 27, spectral data is first converted to a continuoustwo-dimensional quality variable chart, which quality variable chart isfurther analysed to determine the properties of the object 11, 16, 17and/or to detect defects in the object, and to recognize the causes ofsaid phenomena. The data processor 27 can be, for example, amicrocomputer or the like, which is equipped with software suitable forthe purpose.

The data processor 27 of the spectrum separating measurement device 10can further be arranged in a data transmission connection 13 with theother equipment controlling the processing of the web 11. This makes itpossible, for example, to make adjustments automatically on the basis ofmeasurement results determined from the quality variable chart. By meansof the data transmission connection 13, it is also possible to implementalarming of the user or other measures when certain predetermined limitvalues are exceeded.

Preferably, the data processor 27 is equipped with a user interface,such as a display and a keyboard, for displaying data to the user andfor receiving settings and function commands from the user.

In order to synchronize the quality variable chart according to theinvention with the movement of the object 11, 16, 17 being measured, thespectrum separating measurement device 10 is connected with a meansmeasuring the speed of motion of the object. According to FIG. 1 saidmeans can be, for example, in contact with the web 11, being a pulsesensor 15, which is installed in the core of a roll 14 rotating at aperipheral speed corresponding to the rate of propagation of the web.The pulse sensor 15 is arranged to produce one or more pulses for eachone rotation of the roll 14. When the peripheral length of the roll isknown, it is possible to determine the exact rate of propagation of theweb 11 on the basis of the pulses obtained from the pulse sensor 15.

Alternatively, the spectrum separating measurement device 10 and thedata processor 27, incorporated in it, may obtain the data about thespeed of motion required for the synchronization via the datatransmission connection 13 from the equipment controlling the processingof the web 11, such as, for example, the control system of a papermachine.

The spectrum separating measurement device 10 can be arranged to measurethe web 11 (or another object) across the entire so-called productionwidth of the web in the cross-machine direction, or the measurement canalso be focused on a narrower range than the production width.

In position B in FIG. 1, the spectrum separating measurement device 10is arranged to measure the surface of a roll 16 in synchronization withthe rotational speed of the roll 16 in such a way that a continuousquality variable chart about the surface of the roll 16 is recorded inthe data processor 27. As a result of the synchronization, it ispossible to separate from the continuous quality variable chart asection corresponding to each one rotation of the roll 16 to a so-calledmatched two-dimensional quality variable chart. In such successive andmatched quality variable charts, the same specific point in thetwo-dimensional chart will thus always correspond to on and the samespecific point on the surface of the roll 16. The matched qualityvariable charts can further be analysed with the data processor 27, forexample, by averaging said quality variable charts in such a manner thatin successive and matched charts the quality variables corresponding tothe same point in the object, i.e. for example moisture values, areaveraged with each other.

In position C of FIG. 1, the spectrum separating measurement device 10is arranged to measure a moving texture 17 interacting with the web 11in a way synchronized with the speed of rotation of the texture 17. Thetexture 17 can be, for example, a so-called drying felt or wire.According to the invention, a continuous quality variable chart, forexample a moisture chart, is now formed in the data processor 27 in thesame way as above. From this continuous quality variable chart, it isfurther possible to distinguish single matched quality variable chartscorresponding to one rotation of the web 17, for a more detailedanalysis and/or for averaging.

From a two-dimensional quality variable chart determined with a goodtemporal and spatial resolution, it is now possible, according to theinvention, to detect phenomena occurring only momentarily or also morecontinuously in the machine direction. In the following, the analysis ofquality variable charts formed according to the invention will bedescribed in more detail, now with reference to FIGS. 4 to 6.

FIG. 4 presents, in principle, a continuous 2-dimensional qualityvariable chart 40 according to the invention. The chart mentioned inthis example can be considered to be formed with the spectrum separatingmeasurement device 10 placed in position A in FIG. 1 and bysynchronizing the imaging with the movement of the web 11. In thefollowing, the moisture level of the web will be used as an example ofthe quality variable being monitored, in which case the wavelengthsmeasured by the measurement device 10 are selected appropriately forthis purpose from the near infrared range.

In the following examples, the quality variable chart 40 thus describesthe local distribution of the moisture level of the web 11 across agiven length of the web 11. In the quality variable chart 40 of FIG. 4,the horizontal direction (the first dimension) thus corresponds to thedifferent regions of the web in the machine direction, and the verticaldirection (the second dimension) correspondingly to the differentregions of the web in the cross-direction.

In the continuous quality variable chart 40, the areas marked with blackovals 41 and black rectangles 42 as well as light circles 43 ofdifferent sizes indicate points at which the moisture detected by thespectrum separating measurement device 10 differs within the measuringaccuracy from the moisture of the background 44 of the quality variablechart 40 illustrated as white. It is obvious that in reality, thebackground 44 of the quality variable chart 40 consists of a largenumber of points and areas differing from each other to some extent intheir moisture level. Similarly, for example recurrent areas 41 markedwith black ovals do not recur in exactly the same size and moisturelevel at different parts of the quality variable chart 40. Primarily forreasons of the drawing technique and clarity, the background 44 and theareas 41, 42, 43 in FIG. 4 are illustrated with simplified shapes andmoisture levels.

In this example, the areas 41 recurring in the continuous qualityvariable chart 40 of FIG. 4 are caused by local damaging/soiling 41′ ofthe coating of the roll 16 shown in FIG. 1. In a corresponding manner,the areas 42 are caused by local damaging/soiling 42′ of the texture 17shown in FIG. 1. The areas 44 indicate minor random moisture changesoccurring in the web 11 for various reasons.

According to the invention, the continuous quality variable chart 40 cannow be analysed by dividing it into matched quality variable charts andfurther by averaging the matched quality variable charts with eachother. The cycle length of the matched quality variable charts, whichcorresponds to the direction of propagation of the web 11, is selectedon the basis of the part or means with which the web 11 is in contact inits path and about which more data is needed.

FIG. 5 shows an averaged matched quality variable chart 50, which isformed by dividing the continuous quality variable chart 40 into partialcharts 47 having the length of a cycle 45. In this case, the length ofthe cycle 45 now corresponds to the peripheral length of the roll 16.

To form the averaged and matched quality variable chart 50, the partialcharts 47 are averaged together in such a way that the pointscorresponding to the same pixel in successive partial charts 47 areaveraged together. In other words, in this example, the same pixel inthe successive partial charts 47 always corresponds to the same point onthe surface of the roll 16. In the matched quality variable chart 50obtained as a result of the averaging, the moisture deviation caused bydamaging/soiling 41′ of the roll 16 is detected as a distinctive area41′″ whose moisture differs from the moisture of its environment.However, local damaging/soiling 42′ of the texture 17 is detected as aweaker, streak-like phenomenon 42′″ occurring across the whole averagedquality variable chart 50. The reason for this is that when theperipheral length 45 of the roll 16 is used as the cycle length in theaveraging, the cycle of occurrence of the damaging/soiling 42′ of thetexture 17 does not correlate with said cycle length 45.

FIG. 6 shows an averaged and matched quality variable chart 60 formed ina corresponding manner by dividing the continuous quality variable chart40 into partial charts 48 according to a cycle length 46. Now, when thecycle length 46 correlates with the cycle of occurrence ofdamaging/soiling 42′ of the texture 17, the corresponding moisturedeviation 4′″ is clearly visible in the averaged quality variable chart40. In this situation, the change in the moisture level caused in theaveraged and matched quality variable chart 40 by areas 41 occurring atcycle lengths 45 in the continuous quality variable chart 60 is, inturn, distributed in a corresponding manner across the areacorresponding to the entire length of the quality variable chart 60.

Moisture deviations 44, which occur at random in the continuous qualityvariable chart 40 and do not correlate with the cycle lengths 45, 46used in the formation of matched quality variable charts 50 and 60, arelevelled out in the averaged quality variable charts 50 and 60 asbackgrounds 51 and 61. Using a sufficiently long averaging, it is thuspossible, in the method according to the invention, to efficientlyreduce random noise occurring in quality variable charts. Such randomnoise occurs, for example, in a situation, in which the measurement isdisturbed by water mist or water spraying occurring between the spectrumseparating measurement device 10 and the object 11, 16, 17 to bemeasured. Such a situation is typical when the measurement is performed,for example, in the wet end of a paper machine. Random noise can also becaused by the spectrum separating measurement device 10 itself, whereinthe amount of light available for use in measuring spectral data issmall.

The averaging, which improves the accuracy of measurement results, canalso be performed in such a manner that the spectral data, which iscollected in a synchronized manner in relation to the movement of theobject being measured, is averaged in a matched manner even before thequality variable being observed is determined of the spectral data inquestion. This type of averaging of a “raw” signal improves themeasuring accuracy especially in such a situation, where thesignal/noise ratio of the spectral data received as a result of anoptical spectrum separated measurement is weak. Such a situation mayarise, for example, when spectral data is to be measured with a greatspatial, temporal and wavelength resolution, in which case the amount oflight coming to the detector/detectors is small.

Consequently, the method according to the invention makes it possible todetect the cause of the phenomena detectable at a measuring object, suchas web 11, on the basis of the recurrence of said phenomena. Thephenomena may be caused by means located immediately before themeasuring point, or also by means located farther away from themeasuring point. Typically, a “mark” caused in the web 11 by a meanslocated farther away from the measuring point is, to some extent, fadedwhen arriving at the measuring point; therefore, its detection willtypically require the longer averaging, the farther away from themeasuring point the means causing the mark is located.

Although the invention has been described above primarily for thepurpose of detecting transient spot-like defects in the direction ofmovement of the object to be measured, it is obvious that the inventioncan also be used to detect various defects of longer duration orextending longer in the direction of movement, i.e. streak-like defects.In a streak-like defect, which is continuous in the direction ofmovement, the recurrence of the defect in the direction of movement andthereby the cause of the defect can be identified, for example, asrecurrent variation in the width of the streak and/or as recurrent“twisting” of the streak in the direction transverse to the direction ofmovement. In discontinuous streaks, i.e. streaks occurring as stretches,the recurrence can be identified, for example, on the basis of themoments of starting and/or ending of the streak.

Further, the defects detectable by means of the method can be, in thesame way as spots, narrow in the cross-direction, or the defects canalso extend to a wider range in the cross-direction, all the way to theproduction width. Wider defects in the cross-direction, which aredetectable by the method may include, for example, whipping of the web,which will be discussed in more detail in connection with theembodiments of the invention herein below.

Thus, the only precondition, which is substantial in view of theinvention, is that some kind of recurrence in the direction of movementcan be identified in the defect to be detected on the basis of a localdeviation in the quality variable being examined, by means of whichrecurrence the cause of the defect can be further determined.

Preferably, the measurement according to the invention is performed insuch a way that a portion of the continuous quality variable chart 40with a certain length is recorded in the memory of the data processor 27of the spectrum separating measurement device 10. After this, thecontinuous quality variable chart 40 stored in the memory is analysed bydividing it into matched partial charts 47, 48 having the length of agiven cycle. The matched partial charts 47, 48 can further be averagedto form averaged and matched quality variable charts 50, 60. Asmentioned before, averaging can also be performed on spectral data, inwhich case the quality variable for a matched quality variable chart isdetermined only after averaging of a “raw” signal. The cycle length 45,46 to be used in the formation of matched quality variable charts can beselected of predetermined cycle lengths which have been stored in thememory of the data processor 27 and which correspond to the peripherallengths of different rotating/moving rolls or textures, or the like, inthe apparatus to be monitored. The continuous quality variable chart 40is analysed by using said known different cycle lengths one after theother.

Alternatively, it is also possible that the data processor 27automatically scans different cycle lengths at a range determined by theuser, looking for any cycle length at which an obvious correlation isdetected in the averaged and matched quality variable chart 50, 60. Whensuch a correlation is detected, an attempt is made to identify its causeon the basis of the corresponding cycle length from the data about theprocess apparatus stored in the memory of the data processor 27 inadvance. If necessary, the user is also informed of the correlation.

Naturally, it will be obvious for anyone skilled in the art that thedata processor 27 can be implemented in such a way that a continuousquality variable chart 40 stored in the memory of the data processor 27is efficiently processed by using, for example, several cycle lengths45, 46 simultaneously in parallel in the computation. This can beimplemented, for example, by two or more processors operating inparallel and analysing, by different methods, the same continuousquality variable chart 40 stored in the memory. Further, the dataprocessor 27 can also be implemented in such a way that when analysingthe continuous quality variable chart 40 stored in the memory, thesignal generated by the spectrometer 25 is simultaneously stored inanother location in the memory of the data processor 27, in which caseno measuring information produced by the spectrometer 25 is lost duringsaid analysis. Said embodiments make it possible to produce measuringinformation about the object to be measured substantially in real time,which will further make it possible to quickly intervene in the processto be monitored, automatically or manually by the user.

Embodiments of the Invention

In the following, some embodiments will be presented to exemplify theapplication of the method according to the invention in processes formanufacturing and/or finishing paper, board, or a correspondingmaterial.

A local blockage or damage in a texture used for drying a fibre web,such as a drying felt, can be detected by direct measurement, accordingto the invention, of the surface of the drying felt. Thus, a localdeviation in, for example, the moisture level will be detected in thematched quality variable chart of the felt recorded during its singlerotation, or in a matched and averaged quality variable chart computedon the basis of several rotations. The same malfunction of the dryingweb can also be detected on the basis of the recurrent “marking” of thedrying web in the passing fibre web, by measuring the fibre web to beprocessed. At that point of the fibre web, which corresponds to theblocked point in the felt, or the like, the moisture of the web differsfrom the moisture in the surrounding area of the web, which is detectedas a deviation in the quality variable chart. The farther away from thecomponent causing the defect the measurement of the web is taken, thelonger the averaging which is typically required to detect thephenomenon, because it fades as the distance becomes longer.

By measuring the drying felt or another texture interacting with theweb, or the marking caused by said texture in the web, it is alsopossible to detect, for example, malfunctions of washing sprays cleaningsaid texture, and/or defects in the cross-direction profile of the presssection pressing the texture and the web against each other. Typically,a defect in the cross-direction profile of the nip between two oppositerolls in the press section may be caused, for example, by curving of therolls in the direction of the longitudinal axis (incorrect crowning) orby dirt or other material adhered locally to the surface of the rolls.

Among other things, it has been found in tests performed on a test papermachine that with the method according to the invention it is possibleto detect the effect of high pressure water jets used in washing thefelts of a paper machine on the moisture profile of the paper web, whichinteracts with the felts.

The effect of nip vibrations, i.e. unfavourable temporal changes in thenip force, can be detected in the quality variable chart as so-calledwhipping of the texture or the web to be processed, which passes throughthe nip. Whipping refers to the formation of stripes in thecross-direction in the object being examined, caused by temporalvariations in the nip force and thereby further, for example, variationsin the drying capacity. The cycle length of nip vibrations is typicallysignificantly shorter than the peripheral length of the rolls formingthe nip.

The textures used in manufacturing and/or finishing processes of paperand/or board, in connection with which the method of the invention canbe applied, include not only the above-mentioned drying felt but alsovarious wires and belt rolls. By means of the invention, it is alsopossible to detect obstructions in the suction roll on the basis of amarking caused by the suction roll in the fibre web, by synchronizingthe measurement of the fibre web with the rotation of the suction roll.

The method of the invention is also suitable for controlling thecondition of so-called soft rolls, which are coated. Soft rolls areused, for example, in the calendering of paper, wherein the paper web isguided through one or more so-called calender nips. The calender nip isformed between a hard-faced metal roll and a soft-faced coated roll. Thenip can also be formed between two soft-faced rolls. In soft-faced rollsused in modern calenders, the metal roll frame is typically coated witha polymer material. The polymer coating of the roll may be damagedduring the use, for example, when extra solid material is passed throughthe nip, causing a momentary and local increase in the nip force, a kindof a pressure impact, which damages the roll coating locally. Thecoating damage can also be caused by the temperature of the coating,which increases, for some reason, locally to a level, which is too highfor the polymer material used. Factors affecting the temperature of thecoated roll include, for example, a change in the heat transferproperties caused by a dirt layer adhered to the roll, or other changesin the nip contact, particularly when heated backing rolls are used.

Using the method according to the invention, the condition of thesoft-faced roll can be monitored by measuring the surface of the roll insynchronization with the rotation speed of the roll and thereby forminga matched two-dimensional quality variable chart of the surface of theroll in accordance with the invention. If necessary, several matchedquality variable charts corresponding to one rotation of the roll can beaveraged, as described above. Defects in the roll coating are detected,for example, as reflecting characteristics differing from thesurrounding roll coating either as local areas of roll coating, aswhipping of the roll coating, or as variations across the whole width ofthe roll in the machine direction.

Applying the method of the invention, it is also possible to detect, inconnection with coated rolls, such transient phenomena, which cannot beproperly detected by methods of prior art. Such phenomena include, forexample, in the processing of a coated paper web, local variations inthe quantity of coating material carried by the paper web onto the roll,that is, so-called wet coating spots, coating streaks or other transientcoating defects. When passing through the calender nip and adhering tothe coated roll, such coating defects may cause not only a variation inthe quality of the final product but also actual damage to the rollcoating.

When applying the method of the invention, it is possible to detect sucha problematic situation quickly and thereby to reduce the probability ofcausing a coating defect or to prevent the coating damage from becomingworse. Quick detection of the problematic situation will also reduce theproduction of a final product of poor quality.

By means of data obtained about the condition of the coated rollsubstantially in real time, it is also possible to plan the maintenanceof the rolls better and to avoid unforeseen and unnecessary stoppages.The condition of the roll coatings can also be controlled by measuringthe fibre web to be processed, wherein defects occurring in rollcoatings are detected by means of recurrent marking of the fibre web.The control of the fibre web by imaging has the advantage thatmeasurements made at one measuring point can thus be used to control alonger web length. For example, in a calender, the condition of severalsoft rolls can be monitored by means of one measuring point placed afterthe calender.

Furthermore, the invention is also suitable for detecting local defectsin the coating of a coated web. Thus the measurement can be performed,for example, on a visible wavelength range as a reflection measurement,in which case a local defect in the coating of the web is detected as adeviation in the intrinsic reflectance factor of the web.

By means of the present invention, it is thus possible to control, in aconsiderably more versatile way than before, various properties ofcomponents used in processes for manufacturing or finishing a fibre web,as well as properties of the web to be manufactured or finished.

At a certain measuring point, the measurement width can be selected tobe suitable for each case. The measuring can be performed in a directiontransverse to the direction of movement of the object, for example foran area with the width of one meter, which area is moved in thecross-direction alternatively at different locations of the productionwidth. Momentarily, the measuring can be extended to take place acrossthe full width of the web, wherein it is also possible to detect widerdeviations in the cross-direction. At a certain point of the web, inorder to more accurately analyse the phenomenon detected in itscross-direction, the measurement can be focused on said cross-directionarea only.

Thanks to the synchronization with the movement of the object to bemeasured, the method of the invention can also be applied in a situationin which the movement of the object is accelerating or decelerating.

By combining the modes and apparatus structures presented in connectionwith the different embodiments of the invention presented above, it ispossible to provide various embodiments of the invention, which complywith the spirit of the invention. Therefore, the above-presentedexamples must not be interpreted as restrictive to the invention, butthe embodiments of the invention can be freely varied within the scopeof the inventive features presented in the claims herein below.

For example, the spectrum separating measurement device used in themethod according to the invention can naturally be implemented also inother ways than that presented in FIG. 2. By arranging, for example, anadequate number of measurement devices known from publication WO99/14579 in parallel in the cross-direction of the object beingmeasured, it is possible to collect spectral data required to form aquality variable chart according to the invention from the object. Themeasurement can, if necessary, be implemented also without using opticalfibres.

In addition, the spectrum separating measurement device (or devices)used in the measurement can further be based on, instead of the use of aspectrograph 30 and a matrix detector 31 or corresponding components,the use of parallel optical filters and separate detectors installedafter them, for example, in the manner presented in U.S. Pat. No.3,641,349.

A measurement applying the method according to the invention is notlimited only to measurements taken in the infrared range, but dependingon the quality variable being examined, the wavelength range beingmeasured can be freely selected according to the application inquestion. When the quality variable being examined is the moisture levelor the amount of coating of a paper web, the measurements are takenadvantageously on the infrared wavelength range. When measuring thecharacteristics of the coating, the measuring wavelengths can beselected to correspond to the wavelengths characteristic to cellulose,lime or latex. When measuring the colour, brightness, glare orsmoothness of the paper web, or the condition of the roll coating, themeasurement can be performed, for example, in the visible wavelengthrange as well. The measurements can be performed, according to the needin each case, for example, on the upper or lower surface of a felt orthe web.

According to the invention, spectral data on the object being examinedcan be collected by measuring electromagnetic radiation, which hastransmitted, reflected or otherwise emitted by the object. The lightsource or sources possibly required in the measurement are thus placedin a manner suitable and appropriate for each method of measurement.

It is obvious that that the two-dimensional quality variable chartspresented as functions of locations in FIGS. 4 to 6 can also bepresented as so-called three-dimensional quality variable charts, inwhich case, at each point of the two-dimensional chart, the value of aquality variable is graphically represented on its own third coordinateaxis.

1. A method in the process for manufacturing and/or finishing a fibreweb, in which method said continuous and moving web, and/or a movingmeans related to the processing of the web, and is monitored by at leastone optical spectrum separating measurement device to determine at leastone quality variable of said object for the purpose of controlling thequality or condition, wherein from the object being monitored and beingin a propagating and/or rotating movement, spectral data, synchronizedwith the movement of the object, is collected by measuring theelectromagnetic radiation, which has been transmitted, reflected orotherwise emitted by the object, in a temporally and spatially resolvedmanner with said at least one optical spectrum separating measurementdevice, on the basis of spectral data, a two-dimensional qualityvariable chart is formed, which is substantially continuous in thedirection of movement of the object and which presents at least onequality variable of the object as a function of the position, in orderto determine the properties of the object and/or defects in the object,local deviations and/or discontinuities are detected, especially in thedirection of movement of said continuous quality variable chart, andthat the cause of said deviations and/or discontinuities is identifiedon the basis of the periodicity of said phenomena in the direction ofmovement.
 2. The method according to claim 1, wherein when the object tobe monitored is a moving and continuous web, malfunctioning of the meansrelated to the processing of the web is detected on the basis of aperiodical marking caused by said means in the passing web and visiblein the quality variable chart formed of the web.
 3. The method accordingto claim 1, whereinin order to analyse the continuous quality variablechart, the continuous quality variable chart is formed as successivematched partial charts having the length of a given cycle.
 4. The methodaccording to claim 3, wherein the cycle length to be used in theformation of the matched partial charts is selected to correspond to thelength of influence specific to the means related to the processing ofthe passing web, such as, for example, the length of the periphery/shellof the means in the direction of movement, or, in the direction ofmovement, the impact length characteristic to the vibration of saidmeans or a corresponding interference.
 5. The method according to claim3, wherein the cycle length to be used in the formation of the matchedpartial charts is selected from a range determined by the user, bysearching for such a cycle length with which a distinct deviation and/ora discontinuity in the quality variable is detected in the matchedquality variable chart.
 6. The method according to claim 3, whereinwhenforming matched partial charts, the spectral data is averaged across thecycle length used in forming the partial charts.
 7. The method accordingto claim 3, whereinthe successive matched partial charts are furthercombined to form an averaged and matched quality variable chart.
 8. Themethod according to claim 1, wherein the quality variable chart isformed of the object in a cross-direction in relation to its directionof movement on the basis of cross-directional profiles of spectral datameasured at successive moments of time, in which case an individualcross-directional profile comprises, in the direction transverse to themovement of the object, parallel measuring points, a substantiallycontinuous spectrum or wavelength bands separated from a continuousspectrum in a certain wavelength range being stored at each measuringpoint.
 9. The method according to claim 8, wherein all the parallelmeasuring points of an individual cross-directional profile and all thewavelengths measured at each measuring point are stored substantiallysimultaneously.
 10. The method according to claim 8, wherein anindividual cross-directional profile covers substantially the entirewidth of the object in the cross-direction at once.
 11. The methodaccording to claim 1, wherein the method is used to monitor fibre web orits coating.
 12. The method according to claim 1, wherein the method isused to monitor a texture, such as a wire or a felt, used in connectionwith the processing of the web.
 13. The method according to claim 1,wherein the method is used to monitor a roll, suction roll, or rollcoating used in connection with the processing of the web.
 14. Themethod according to claim 1, wherein the method is used to monitor areel or the like formed of the web.
 15. The method according to claim 1,wherein the quality variable monitored by the method is the moisturelevel or the quantity of coating.
 16. The method according to claim 1,wherein the electromagnetic radiation, which has been transmitted,reflected or otherwise emitted by the object, is measured substantiallyon the wavelengths of an infrared or near infrared range.
 17. The methodaccording to claim 1, wherein the electromagnetic radiation, which hasbeen transmitted, reflected or otherwise emitted by the object, ismeasured substantially on the wavelengths of the visible range.
 18. Themethod according to claim 1, wherein on the basis of the phenomenadetected by the method, the process for manufacturing and/or finishingthe web is controlled, and/or the need for maintenance of the means andcomponents used in said processes is evaluated by the user orautomatically.